This invention relates to a roof for a metallurgical ladle/furnace with a facility for fume extraction.
Such a roof for a ladle arc furnace (L.A.F.) comprises a self-supporting structure of metallic pipework defining at least one cooling water circuit, with three apertures in its central region each to accommodate a carbon electrode.
It is essential to collect, and dispose of, fume emitted from the melt during processing and one proposal is to collect some two thirds of the fume volume from a peripheral collection collar, with some one third collected by draw-off through an annular gap around each electrode. In practice, and particularly because of the use of circular section metallic pipework, peripheral collection soon becomes ineffective due to slag splash, which results in a build-up of slag that throttles or blocks inlet apertures to the collar, resulting in extensive volumes of fumes exiting via the annular gaps. Apart from the gaps having, a finite flow capacity, serious wear is effected by the fume/gas flow and acceleration of particulates on the relatively expensive electrodes. In addition, such roofs must be frequently removed, ideally before the combined weight of the roof and slag exceeds the lifting capacity of the associated lifting equipment, for manual removal of the slag build-up with air hammers and similar chisel tools, during the course of which the pipework is frequently damaged, if only by deformation rather than puncture, resulting in a reduced tube cross-section and throttled water flow, whereas L.A.F. roofs must have a predetermined water flow rate if they are not to be the subject of cracking and premature failure due to overheating.
A basic object of the invention is the provision of an improved L.A.F roof.
According to the present invention there is provided a roof for a metallurgical ladle/furnace (L.A.F) comprising a self-supporting structure of metallic pipework defining at least one flow circuit for cooling water, with a lower end having a circular peripheral flange characterised in that:
(i) a cylindrical body member of smaller diameter than the flange is located above the flange (in use away from the ladle/firnace), and is provided with an end wall having a plurality of apertures each to receive, in a gas-tight manner, a carbon electrode, and
(ii) an aperture for fume extraction is provided in the arcuate wall of the cylindrical body member.
Compared with prior art proposals, no fume extraction at all occurs via annular gaps surrounding the electrodes where the electrodes enter the roof, and hence no abrasion and resulting loss of carbon from the electrodes occurs as a result of fume extraction. In addition, as the arcuate wall of the cylindrical body member would normally extend vertically, and as its aperture(s) is more distant from the melt than prior art proposals, the propensity for splashed slag to rise as far as the aperture of the cylindrical body member and there adherence resulting in slag build up and aperture restriction or eventual blockage is remote if not impossible.
The roof is assembled wholly or principally from rolled, rectangular hollow sections, with adjacent sections secured together by welding. The use of such sections, precludes the adherence of slag, in contrast to prior art roofs of circular section tubing that present xe2x80x9cshelvesxe2x80x9d that encourage the adherence and accumulation of slag.
The hollow sections are bent to the required curvature and water flow passages cut into adjacent section for zig-zag water flow, in the known manner.
The roof has one water circuit, two water circuits extending over 180xc2x0 segments, three water circuits extending over 120xc2x0 segments, or four water circuits extending over 90xc2x0 segments, depending on a number of design factors.
The cylindrical body member has plural fume exit apertures such as two 180xc2x0 apart, three 120xc2x0 apart or four 90xc2x0 apart. The or each fume apertures is/are connected to ducting to convey the fumes to downstream treatment equipment, such as scrubbers or precipitators.
Interposed between the cylindrical body member and the circular peripheral flange is an intermediate zone.
The intermediate zone is of larger diameter than the cylindrical body member, and of smaller diameter than the flange.
In one embodiment, a transition zone between the lower portion of the cylindrical body member and the upper portion of central zone is completely open.
In another embodiment, the transition zone between the cylindrical body member and the central zone is partly closed off by a fixed or removable wall that, being in use closer to the melt than aperture of the cylindrical body member, serves as a slag splash shield.
The peripheral flange is also apertured for fume take-off peripherally in addition to fume take-off via the cylindrical body member.
The peripheral flange aperture is constructed from rolled hollow section tubing so as to present only vertical or horizontal faces, and no planar or arcuate xe2x80x9cshelfxe2x80x9d that would invite slag build up.